For decades, there have been known devices for generating high-power electromagnetic radiation using electron beams propagating in one or more vacuum tubes.
The most commonly used of these devices are klystrons, magnetrons, backward wave tubes, or traveling wave tubes, which are used for example to generate high-intensity radar beams.
These devices have numerous disadvantages.
In particular, they consume large amounts of energy and remain bulky and fragile due to the presence of the vacuum tubes.
It has also been proposed to apply time reversal methods in order to amplify electromagnetic pulses (for example, see “Generation of very high pressure pulses with 1-bit time reversal in a solid waveguide” by G. Montaldo, P. Roux, A. Deride, C. Negreira, and M. Fink, published in The Journal of the Acoustical Society of America, vol. 110, pp. 2849-2857, 2001).
More particularly, a waveguide is provided that is open at one end (front) and closed off at the other end (rear) by a wall comprising a plurality of piezoelectric transducers.
A pulse is generated at a target point outside the waveguide and propagates into the waveguide by the open front end. Signals are thus captured by the transducers inside the guide, at the rear end, and are representative of the field resulting from propagation of the wave in the waveguide. Because of reverberation on walls of the waveguide, these signals thus have significant temporal spread, for example on the order of 1000 times the duration of the initial pulse. A signal corresponding to the time-reversed signal received is then re-emitted by means of the transducers.
The pulse thus generated has remarkable temporal compression at the target point, and by comparing the signal obtained at the target point with that which would have been obtained without the waveguide (for example when emitted in open water), remarkable gains have been measured (for example on the order of fifteen). The effects of spatial and temporal compression thus provide a pulse of high amplitude.
Such a device thus allows obtaining high-power waves while providing a reduction in weight and an improved sturdiness compared to conventional devices for microwave generation as described above.
However, such a device and such a method have disadvantages. For UHF waves, waveguide has disadvantage of being large in size.
To reduce this size, it has recently been proposed to replace the waveguide by a reverberation cavity able to accommodate a large number of reflections of an electromagnetic wave propagating inside the cavity, as is described for example in “Focusing and amplification of electromagnetic waves by time reversal in a leaky reverberation chamber” by Matthieu Davy, Julien de Rosny, Jean-Christophe Joly and Mathias Fink, published in Comptes Rendus de Physique de l'Académdie des Sciences volume 11, pages 37-43 of 18 Feb. 2010. Such a cavity always has a front opening for emission of the electromagnetic wave. However, for the cavity to enable the implementation of time-reversal techniques, it is necessary to limit the dimensions of the opening in order to maintain sufficiently high quality factor for the cavity.
Therefore, the width of the focal zone obtained at the target point cannot be reduced (diffraction requires enlarging the size of the opening to reduce the focal zone to the target point). In addition, the limited size of the opening also imposes constraints on the angular range which can be covered by the electromagnetic beam emitted.
The present invention is intended to overcome these disadvantages.
Thus, the present invention aims to provide a method and a device for generating high-power electromagnetic radiation, having a reduced size, greater sturdiness, and high reliability, while providing a greater focus and a large angular range.